It's prolly just a beta glitch or what not, but it's basically just a purple sphere that floats and reacts to players. So me and two friends ended up getting all the players in our tower to play soccer with it and finally knock it off the edge lol. Just proves how great the game is when you and a few friends can get a whole group of strangers to unite for a common goal without saying a single word..it's the power of the dance off Great game Bungie!